Creating a "bubble" shape lense for goggles
If you have a nice number of vertices in the perimeter ( I think you do.. 12 on each side of the triangle?)

Then:


One inset
Delete inner face, and select new perimeter
CtrlF (Face Menu) > 'Grid Fill'..




.. can give you a nice topology, in which you can select a central vertex, and 
 O Proportionally Edit it. Set the Transform Orientation to 'Normal', and GZZ bulge the vertices outwards.

If you need to conform to existing geometry, you can hide the outer edge-ring (blue in the picture) while you're doing the proportional edit.

If when you unhide the outer ring the transition is too sharp, you can select  all but the vertices on the perimeter and  CtrlV > 'Vertex Smooth' them.